The known pumps which are used in this type of application generally comprise a body which delimits a metering chamber provided in the lower part with an intake orifice and having in the upper part an opening into which there is introduced a sleeve borne by an axially displaceable actuation head which is provided with a discharge conduit and with a closure element and which moreover cooperates with a return spring mounted on the exterior of said body.
This arrangement makes it possible to prevent the spring, which is made of metal, from entering into contact with the product and giving rise to physico-chemical degradation phenomena.
The displacement of the actuation head relative to the body has a piston effect which causes the product inside the chamber to be compressed and to exit via the discharge conduit.
The intake orifice is for its part able to be closed off, at least during the phase of dispensing the product, by a valve which is generally a ball valve.
However, this valve is independent of the other constituent elements of the pump and is made in the form of parts which are attached to the body, which creates problems with regard to sealing, coordination during operation and assembly difficulties.
Furthermore, such a valve is subject to the forces of gravity and may fail to operate in the case when the pump is used in the inclined or inverted position.